The present invention relates to a process and means for producing a suspension of a powdery substance and a reaction gas by causing the powdery substance to fall as an annular flow into a reaction space and by conducting the reaction gas downwardly encircling the annular flow of powdery substance.
In order to introduce a suspension of reaction gas and powdery substance into a reaction space two different principles have been applied heretofore, according to which the suspension is formed either before the injecting means or by the aid of the injecting means itself. The first procedure is employed in conventional coal dust burners of coal dust firing installations or in such metallurgical equipment where the pneumatically transported finely divided ore or concentrate is blown, together with its carrier gas, directly into the reaction vessel. When applying this method, the blowing speed at the introduction has to be adjusted to be such that no backfiring of the reactions can occur.
In the event, however, that high degrees of preheating are used the forming of the suspension must be performed as close to the reaction space as possible. The same is true in cases in which the suspension that is being formed is highly reactive, as is for instance the mixture of metallurgical sulfide concentrate and technical oxygen. It is indicated in such cases to perform the suspending not until in the reaction space itself.
The object of the present invention is to provide a suspension forming process wherein first contact between the reacting substances takes place in the reaction space itself, whereby the process is suitable to be used also in the suspension of highly reactive substances.
The literature contains numerous presentations of how a suspension is fed. The majority thereof deals either with the direct introduction by blowing of a pneumatically transported fine solid or with apparatus wherein a suspension jet is formed in ejector-like fashion with the aid of pressure pulsations generated in the reaction gas and is blown into the reaction space. Such a jet constitutes a cone having an aperture angle on the order of 15 to 20 degrees and wherein the solid content is highest in the centre of the jet. The shape of the distribution is primarily dependent on the properties of the solid substance and on the flow velocity of the suspension. In the commonly used case of a cylindrical reaction space, such as the reaction shaft of a flash smelting furnace, the admission of a conical jet of this type is low, as will be demonstrated in greater detail later on.
There are in principle two ways in which the admission may be improved: it is possible to increase the number of supply points, or to form several cones, or one may increase the aperture angle of the jet by imparting to the gas a velocity component directed sideways. In case the suspension is constituted by reactive substances, it is advantageous to form the suspension not until in the immediate vicinity of the reaction space or most advantageously in the reaction space itself.
The proportion of solid matter in the mass of the suspension is usually significant, particularly so in metallurgical applications. Depending on the thickness of the roof lining of the reaction space, on the placement of the supply means and other similar circumstances, the solid matter has to pass through a distance of fall before it reaches the point where the suspension is formed and therefore its vertically directed quantity of motion is significant. In the suspension forming methods of prior art the solid matter tends by this quantity of motion and by its mass inertia to damp the horizontal velocity component possessed by the gas and thereby to cause a narrowing of the jet.